1. Field of the Invention
The present invention generally relates to a body structure of floor parts in a vehicle.
2. Description of Related Art
A variety of body structures with frame construction, which bears an external force applied to a vehicle body, have been proposed and developed for motor trucks and the like.
For example, Japanese Utility Model Provisional Publication No. 4-98683 discloses a ladder frame, which is constructed by connecting a pair of side frames extending along the longitudinal side by a plurality of cross members. A body is mounted on the ladder frame.
On the other hand, passenger cars, which are required to be lightened, have a monocoque structure in which the entire body bears an external force applied to the body. A floor pan is reinforced by a variety of members arranged along the longitudinal side and the crosswise side to ensure the strength required in the case of a frontal impact and a side impact. For example, FIG. 7 shows a section of a vehicle with an ordinary monocoque structure. As shown in FIG. 7, a pair of right and left side members 101 (FIG. 7 only shows one side) arranged along the longitudinal side are welded to the bottom surface of a floor pan 102 (the welded part is denoted by Z) to thereby reinforce the floor pan 102 along tie longitudinal side. A cross member 104, which is formed by pressing, is welded between a tunnel part 102a at the center of the floor pan 102 and a pair of right and left sills 103 (the welded part is denoted by Y) to thereby reinforce the floor pan 102 along the crosswise side.
In the vehicle with the monocoque structure, the cross member 104 is divided into two parts across the tunnel part 102a, and this makes it impossible to acquire the sufficient strength of the cross member 104. Moreover, the cross member 104 is welded to the side sills 103 by abutting the outer end of the cross member 104 against the side of the side sills 103. Therefore, the welded part has a low rigidity. In order to ensure the sufficient strength, there is the necessity of adding reinforcement materials, increasing the number of cross members 104 or increasing the board thickness of the cross member 104, the floor pan 102, the side sill 103 or the like. This results in the increase in the vehicle mass. It is necessary to change the length of the cross member 104 according to the vehicle width if a plurality of car models with different widths have a floor part called a platform comprised of common parts. Since the cross member 104 is formed by pressing, however, there is the necessity of individually forming the cross member 104 by using a die corresponding to the length of each cross member 104. This results in the increase in a manufacturing cost.
It is therefore an object of the present invention to provide a body structure, which ensures a sufficient vehicle strength to achieve the effect of the monocoque structure to the full without increasing the vehicle mass, and which easily copes with the change in the vehicle width or the like if a common platform is used for a plurality of car models.
The above object can be accomplished by providing a body structure comprising a floor panel member composing a floor surface of a vehicle, a pair of side sills having closed sectional forms and being integrated with both sides of the floor panel member along the width of the vehicle, a pair of first members integrated with the bottom surface of the floor panel member in such a manner as to extend along the longitudinal side of the vehicle; and a plurality of second members integrated with the pair of first members and fixed on the bottom surface of the floor panel member by welding with both ends of at least one second member respectively penetrating into the pair of side sills. Since the second members are continuously formed along the width of the vehicle, and this achieves a sufficient strength. Therefore, there is no necessity of providing any reinforcement materials at the welded part. Moreover, the second members are fixed on the side sills with a high rigidity by welding in the state of penetrating into the side sills, and thus, there is no necessity of increasing the board thickness of the side sills and the like for the purpose of ensuring the rigidity. In addition, the second members can be manufactured by cutting an existing steel pipe to a predetermined size, and it is therefore possible to cope with the change in the width of the vehicle and the like only by changing the cutting size.